I just finished adding new vacuum lines on the four wheel drive system 2000 ford f150.My four wheel drive works fine on 4x4 high ,but when I go to 4x4 low the system goes crazy.1. I must shift to N TO ENGAGE,2. ALOUD POP NOISE HAPPENS,WITH A GRINDING NOISE.3.THE LOW DRIVE POPS OUT OF LOW.CAN NOT USE 4X4 LOW.HIGH IS WORKING FINE CAN SOMEONE HELP ME.
CGALL

 

#1 is how its supposed to work

 

yes must be in neutral and foot on the brake to put into low

 

ok the shifting works fine When I am in low I drive a few ft and a loud bang happens with a grinding and I belive it pops out of 4 low.4 HIGH SEEMS TO BE WORKING FINE.WHAT IS A FORK AND WHERE IS IT LOCATED?
CGALL

 

Shift fork is inside the front differential, but it's operation doesn't change from 4high to 4low. If it is a problem with 4low then it would more likely be the transfer case at fault